1. Field of the Invention
The present invention relates to a method for manufacturing a sidewall actuator array for an ink jet printhead and, more particularly, to a method for manufacturing a sidewall actuator array for an ink jet printhead using a single or double groove forming step orientated in the poling direction for the sidewall actuators.
2. Description of Related Art
Printers provide a means of outputting a permanent record in human readable form. Typically, a printing technique may be categorized as either impact printing or non-impact printing. In impact printing, an image is formed by striking an inked ribbon placed near the surface of the paper. Impact printing techniques may be further characterized as either formed-character printing or matrix printing. In formed-character printing, the element which strikes the ribbon to produce the image consists of a raised mirror image of the desired character. In matrix printing, the character is formed as a series of closely spaced dots which are produced by striking a provided wire or wires against the ribbon. Here, characters are formed as a series of closely spaced dots produced by striking the provided wire or wires against the ribbon. By selectively striking the provided wires, any character representable by a matrix of dots can be produced.
Non-impact printing is often preferred over impact printing in view of its tendency to provide higher printing speeds as well as its better suitability for printing graphics and half-tone images. Non-impact printing techniques include matrix, electrostatic and electrophotographic type printing techniques. In matrix type printing, wires are selectively heated by electrical pulses and the heat thereby generated causes a mark to appear on a sheet of paper, usually specially treated paper. In electrostatic type printing, an electric arc between the printing element and the conductive paper removes an opaque coating on the paper to expose a sublayer of a contrasting color. Finally, in electrophotographic printing, a photoconductive material is selectively charged utilizing a light source such as a laser. A powder toner is attracted to the charged regions and, when placed in contact with a sheet of paper, transfers to the paper's surface. The toner is then subjected to heat which fuses it to the paper.
Another form of non-impact printing is generally classified as ink jet printing. Ink jet printing systems use the ejection of tiny droplets of ink to produce an image. The devices produce highly reproducible and controllable droplets so that a droplet may be printed at a location specified by digitally stored image data. Most ink jet printing systems commercially available may be generally classified as either a "continuous jet" type ink jet printing system where droplets are continuously ejected from the printhead and either directed to or away from the paper depending on the desired image to be produced or as a "drop-on-demand" type ink jet printing system where droplets are ejected from the printhead in response to a specific command related to the image to be produced.
In a continuous jet type ink jet printer, a pump supplies ink to a nozzle assembly where the pumping pressure forces the ink to be ejected therefrom in a continuous stream. The nozzle assembly includes a piezo crystal continuously driven by an electrical voltage, thereby creating pressure disturbances that cause the continuous stream of ink ejected therefrom to break up into uniform droplets of ink. The droplets acquire an electrostatic charge due to the presence of an electrostatic field established close to the ejection orifice. Using high voltage deflection plates, the trajectory of selected ones of the electrostatically charged droplets can be controlled to hit a desired spot on a sheet of paper. The high voltage deflection plates can also deflect unselected ones of the electrostatically charged droplets away from the sheet of paper and into a reservoir for recycling purposes. Due to the small size of the droplets and the precise trajectory control, the quality of continuous jet type ink jet printing systems can approach that of formed-character impact printing systems. However, one drawback to continuous jet type ink jet printing systems is that fluid must be jetting even when little or no printing is required. This requirement degrades the ink and decreases reliability of the printing system.
Due to this drawback, there has been increased interest in those printing systems in which droplets are ejected from the printhead by electromechanically induced pressure waves. In this type of printing system, a volumetric change in the fluid is induced by the application of a voltage pulse to a piezoelectric material which is directly or indirectly coupled to the fluid. This volumetric change causes pressure/velocity transients to occur in the fluid, thereby causing the ejection of a droplet therefrom. Since the voltage is applied only when a droplet is desired, these types of ink jet printing systems are referred to as "drop-on-demand" type ink jet printing systems.
A typical drop-on-demand type ink jet printing system is disclosed in U.S. Pat. No. 3,946,398 to Kyser et al. In Kyser et al., a pressure plate formed from two transversely expandable piezoelectric plates is utilized as the upper wall of an ink-carrying pressure chamber. By applying a voltage across the piezoelectric plates, the pressure plate flexes inwardly into the pressure chamber, thereby causing a fluid displacing volumetric change within the chamber. Another typical drop-on-demand type ink jet printing system may be seen by reference to U.S. Pat. No. 3,857,045 to Zoltan. In Zoltan, a tubular piezoelectric transducer surrounds an ink-carrying channel. When the transducer is excited by the application of an electrical voltage pulse, the ink-carrying channel is compressed and a drop of ink is ejected from the channel. However, the relatively low channel density achieved by such systems as well as the relatively complicated arrangement of the piezoelectric transducer and the associated ink-carrying channel which characterizes such systems causes such systems to be time-consuming and expensive to manufacture.
In order to reduce the per ink-carrying channel (or "jet") manufacturing cost of an ink jet printhead, in particular, those ink jet printheads having a piezoelectric actuator, it has long been desired to produce an ink jet printhead having a channel array in which the individual channels which comprise the array are arranged such that the spacing between adjacent channels is relatively small. For example, it would be very desirable to construct an ink jet printhead having a channel array where adjacent channels are spaced between approximately four and eight mils apart. Such a ink jet printhead is hereby defined as a "high density" ink jet printhead. In addition to a reduction in the per ink-carrying channel manufacturing cost, another advantage which would result from the manufacture of an ink jet printhead with a high channel density would be an increase in printer speed. However, the very close spacing between channels in the proposed high density ink jet printhead has long been a major problem in the manufacture of such printheads.
Many attempts to manufacture ink jet printheads having piezoelectric actuators and reduced spacing between channels have focussed on the manufacture of ink jet printheads with parallel channel arrays and shear mode piezoelectric transducers for actuating the channels. For example, U.S. Pat. Nos. 4,584,590 and 4,825,227, both to Fischbeck et al., disclose shear mode piezoelectric transducers for a parallel channel array ink jet printhead. In both of the Fischbeck et al. patents, a series of open ended parallel ink pressure chambers are covered with a sheet of a piezoelectric material along their roofs. Electrodes are provided on opposite sides of the sheet of piezoelectric material such that positive electrodes are positioned above the vertical walls separating pressure chambers and negative electrodes are positioned over the chamber itself. When an electric field is provided across the electrodes, the piezoelectric material, which is polled in a direction normal to the electric field direction, distorts in a shear mode configuration to compress the ink pressure chamber. In these configurations, however, much of the piezoelectric material is inactive. Furthermore, the extent of deformation of the piezoelectric element tends to be small, thereby minimizing the pressure pulse which may be applied to the ink by the actuator.
An ink jet printhead having a parallel channel array and which utilizes piezoelectric materials to construct the sidewalls of the ink-carrying channels may be seen by reference to U.S. Pat. No. 4,536,097 to Nilsson. In Nilsson, an ink jet channel matrix is formed by a series of strips of a piezoelectric material disposed in spaced parallel relationships and covered on opposite sides by first and second plates. One plate is constructed of a conductive material and forms a shared electrode for all of the strips of piezoelectric material. On the other side of the strips, electrical contacts are used to electrically connect channel defining pairs of the strips of piezoelectric material. When a voltage is applied to the two strips of piezoelectric material which define a channel, the strips become narrower and higher such that the enclosed cross-sectional area of the channel is enlarged and ink is drawn into the channel. When the voltage is removed, the strips return to their original shape, thereby reducing channel volume and ejecting ink therefrom.
An ink jet printhead having a parallel ink-carrying channel array and which utilizes piezoelectric material to form a shear mode actuator for the vertical walls of the channel has also been disclosed. For example, U.S. Pat. Nos. 4,879,568 to Bartky et al. and 4,887,100 to Michaelis et al. each disclose an ink jet printhead channel array in which a piezoelectric material is used as the vertical wall along the entire length of each channel forming the array. In these configurations, the vertical channel walls are constructed of two oppositely polled pieces of piezoelectric material mounted next to each other and sandwiched between top and bottom walls to form the ink channels. Electrodes are formed along the entire height of the vertical channel walls. When an electric field normal to the polling direction of the pieces of piezoelectric material is generated between a pair of electrodes formed on opposite sides of a vertical wall, both of the oppositely poled pieces of piezoelectric material distort in a first direction to compress the ink channel.
The process by which the electrodes are formed in Bartky et al. and Michaelis et al. for the above-referenced piezoelectric sidewall actuator configurations is simplified by the fact that active material is utilized for the entire height of the sidewalls. Where the entire sidewall is not formed of active material or should not have an electrode deposited thereon, Bartky et al., Michaelis et al. and, with even greater particularity, U.S. Pat. No. 5,016,028 to Temple, the recommended process by which electrodes are to be formed along the sidewalls becomes even more complicated. In such configurations, it is recommended that the channel array should be orientated to the electrode depositing, metal vapor beam such that electrode deposition will only take place along part of each sidewall.
It can be readily seen from the foregoing that it would be desirable to provide improved methods for manufacturing sidewall actuator arrays for ink jet printheads which eliminates, or at least substantially reduces, many of the above-mentioned limitations and disadvantages associated with prior methods for manufacturing channel arrays having partially or fully active sidewall actuators. It is, therefore, an object of the present invention to provide such improved methods of manufacturing ink jet printheads.